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212

A BOOK

OF

BIOTECHNOLOGY

Chapt er

Chapter

8

ENZYMES

INTRODUCTION

An enzyme (from the Greek word “enzymos” meaning “in yeast”) is a biocatalyst. It is partly or entirely a protein that can tremendously increase the efficiency of a biochemical reaction without itself being used up. Although a biochemical reaction will proceed to completion in the absence of an enzyme, the process would be extremely slow – so slow in fact, as to make life as we know it impossible. Thus, it is safe to assume that most reactions occurring in the cells are catalyzed by enzymes. The term “catalyst” is used by the physical chemist to denote a substance which alters the rate of a reaction. Consequently, negative catalysis is possible.

The word is used here in the popular sense, i.e., a substance which accelerates a reaction.

NATURE OF ENZYMES

Enzymes, being organic catalysts, have many of the properties of inorganic catalysts and thus can be characterized as follows :

1. Enzymes are active in extremely small amounts-that is, in a biochemical reaction only a small amount of enzyme is necessary to convert a large amount of substrate to product. The two terms substrate and product signify the starting and ending material of a reaction respectively. The number of moles of substrate converted per minute by

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A BOOK

OF

BIOTECHNOLOGY

Chapt er

Chapter

CHEMISTRY

FOR

2

BIOLOGISTS

INTRODUCTION

Chemistry is the science that deals with the composition and structure of matter and with the transformations that matter undergoes. Chemistry is a rather broad field; at one extreme, in theoretical chemistry and spectroscopy, it borders on physics, and at the other extreme, in organic chemistry, it borders on biochemistry and biology.

ATOMS, MOLECULES, ELEMENTS, COMPOUNDS

All substances, whether gas, liquid, or solid, have certain fundamental characteristics in common. If one could break down any substance into its smallest elemental units, it would be composed of atoms. Although it is difficult to observe atomic structure, atoms are known to consist of a mass of positively charged protons, noncharged (or neutral) neutrons, tiny negatively charged electrons, and other even smaller subparticles. An atom has equal numbers of electrons and protons; thus it has a total charge that is zero. When an atom loses or gains electrons it becomes a negatively or positively charged ion (e.g., Na+, Cl–). The protons and neutrons are found in a central nucleus, and the electons float around the nucleus, like negatively charged satellites attracted to a positively charged planet.

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A BOOK

OF

BIOTECHNOLOGY

Chapt er

Chapter

11

STAINING

INTRODUCTION

The subject of dyes or stains and methods of using them has become one of vast proportions.

The number of dyes available is enormous, and ways of employing stains are almost as enormous as the workers using a particular dye or combination of stains. The preparation and use of stains has all become a science in itself, and there exists a most valuable journal, Stain

Technology, devoted to these and related subjects. Experimenting with new dyes and new staining schedules is a most fascinating occupation, and there is a very great deal yet to be learned about stains and their utilization.

STAINS AND THEIR USE

Although stains were used as early as 1770 in the study of the structure of the wood, it was not until 1839 that Ehrenberg used them to study microbes. Their use depends upon the following properties :

1. The chemical must be chromogenic–in other words, it must possess colour – forming groups in its molecules.

2. The stain must exist as a salt in aqueous solutions–that is, it must break up (dissociate) into positively and negatively charged particles. These are called, respectively, cations and anions. For example, in the case of methylene blue, when placed in an aqueous medium the following chemical reaction occurs :

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CHROMOSOMES

AND

DISEASE

Chapt er

Chapter

CHROMOSOMES

AND

191

7

DISEASE

INTRODUCTION

The congenital malformation called mongolism affects one in approximately 650. Ever since the condition was identified in the 1860’s by the British neurologist John Langdon Down, concerned physicians and investigators had been seeking its cause. For many years, Mongolism was described as a heredity disease, the result of some unknown effects in the “germplasm”.

Investigators dissatisfied with such vague explanations have argued the opposite view that the disease is environmental, and have correlated its incidence with accidents due to the developing embryo during gestation, that is, the period between conception and birth.

The explanation of mongolism is now at hand. The disease is neither typically hereditary nor environmental, as these terms are commonly employed. It arises from a defect in the mechanism by which the heredity material is passed on from parent to offspring. This leaves certain questions unanswered: for example, whether the defect in the genetic mechanism is itself hereditary or environmental in origin. The explanation is nonetheless of great significance, for it is among the first findings to come from direct investigation of the genetic apparatus of the human cell. The techniques of cell genetics have mostly been restricted to more easily studied cells of lower animals and plants.

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